Sevinçli, Haldun2017-10-182017-10-182017Sevinçli, H. (2017). Quartic dispersion, strong singularity, magnetic instability, and unique thermoelectric properties in two-dimensional hexagonal lattices of group-VA elements. Nano Letters, 17(4), 2589-2595. doi:10.1021/acs.nanolett.7b003661530-69841530-6992http://doi.org/10.1021/acs.nanolett.7b00366https://hdl.handle.net/11147/6380The critical points and the corresponding singularities in the density of states of crystals were first classified by Van Hove with respect to their dimensionality and energy-momentum dispersions. Here, different from saddle-point Van Hove singularities, the occurrence of a continuum of critical points, which give rise to strong singularities in two-dimensional elemental hexagonal lattices, is shown using a minimal tight-binding formalism. The model predicts quartic energy-momentum dispersions despite quadratic or linear ones, which is also the origin of the strong singularity. Starting with this model and using first-principles density functional theory calculations, a family of novel two-dimensional materials that actually display such singularities are identified and their extraordinary features are investigated. The strong singularity gives rise to ferromagnetic instability with an inverse-square-root temperature dependence and the quartic dispersion is responsible for a steplike transmission spectrum, which is a characteristic feature of one-dimensional systems. Because of the abrupt change in transmission at the band edge, these materials have temperature-independent thermopower and enhanced thermoelectric efficiencies. Nitrogene has exceptionally high thermoelectric efficiencies at temperatures down to 50 K, which could make low-temperature thermoelectric applications possible.eninfo:eu-repo/semantics/openAccessMagnetic instabilityQuartic dispersionThermoelectricityVan Hove singularityTwo-dimensional materialsArticle2-s2.0-8501742841210.1021/acs.nanolett.7b0036610.1021/acs.nanolett.7b00366